In the previous issue of Critical Care, Ware and

colleagues [1] showed that citrulline (CIT) plasma levels are extremely low in critically ill patients with sepsis and signifi cantly lower in patients complicated with acute respiratory distress syndrome (ARDS). Th us, this study brings the new and important information that CIT depletion may be related to morbid events. In addition, these data form a strong rationale for CIT supple men-tation in intensive care unit (ICU) patients with sepsis. For a long time, CIT was considered just a ‘garbage’ amino acid because it is not included in proteins and is known only as an intermediary in the urea cycle. However, some early classic studies suggested that CIT had a unique metabolism and that its defi ciency might be harmful (reviewed recently in [2]). Th e fact that CIT is almost absent from food (with the notable exception o